1. Field of the Invention
This invention relates to an oral sustained release pharmaceutical preparation. More particularly, this invention is concerned with an oral sustained release pharmaceutical preparation which is prepared as a pharmaceutical preparation comprising lower alkyl ether of cellulose, polyacrylic acid or its pharmaceutically acceptable salt, and active drugs, or a pharmaceutical preparation comprising lower alkyl ether of cellulose, polyacrylic acid or its pharmaceutically acceptable salt, and active drugs together with a foaming agent, so that it may release the active drugs by such slow degrees in the stomach or the intestinal tract as to make it possible to provide an adequate supply of active drugs in enough concentration to display their therapeutic value for many hours.
2. Description of the Related Art
Various proposals have hitherto been made as to so-called sustained release pharmaceutical preparations which are made to sustain the release of the active drugs from the pharmaceutical preparations so that the efficacy of the active drugs may be maintained for many hours.
For instance, Japanese patent publication No. 13092/'62 gives a description of a sustained release pharmaceutical preparation of oral type comprising an active drug and slight soluble acidic carboxyvinyl polymer and Japanese patent publication No. 17324/'67 carries a description of a granule and a tablet which comprise a mixture of such a hydrophilic resin as polyvinyl alcohol and polyacrylic acid and a drug and display the sustained efficacy in the stomach or the intestinal tract. All of these pharmaceutical preparations are made to hold and display the sustained curative power of their active drugs in the stomach or the intestinal tract. There is, however, a probability that, granting it to be true that these sustained release pharmaceutical preparations have the property of releasing the drugs from the preparations continuously for many hours, the preparation themselves pass the site of absorption or action for the drug before the drug is released from the preparation in the body. In such a case, this most advantageous property of the preparation can not be utilized.
Another attempt is also proposed to prolong the residence time of the preparation in the stomach while allowing the preparation to release the drug in the stomach for a long time, thus keeping the effective blood concentration for many hours.
Examples of this sort might be quoted from Japanese Laid-Open patent publication No. 61323/'74 which describes a preparation comprising a core drug coated with a polymer film which has a property of swelling in gastric juice to prevent the preparation from passing through the pylorus because of its increased mechanical bulkiness, thus prolonging its residence time in the stomach; followed up by another patent, Japanese Laid-Open patent publication No. 115910/'76, which contains a description of a preparation which is designed to release the drug through a hydrogel while being made to float in gastric juice by use of a large amount of fatty substance of low specific gravity.
Though these pharmaceutical preparations mentioned above are intended to release the active drugs in the stomach gradually, they involve a good possibility of allowing themselves to move on to the intestinal tract before the release of the drugs is not completed due to such physiological factors as meal, stress, condition of a disease or external causes.
Japanese Laid-Open patent publication No. 121418/'75 describes a pharmaceutical preparation which consists of a hollow material such as foamed polystyrol, hard gelatin capsule, and expanded grain, having a coating formed thereupon and another coating of the drug applied thereon, to make them float and stay in gastric juice. The preparations of this type have a disadvantage of requiring a complicated producing process.
Japanese Laid-Open patent publication No. 76418/'77 gives a description of a pharmaceutical preparation which is coated with a foaming agent mainly comprising bicarbonate by use of a coating material containing the drug, or is coated with a mixture of a foaming agent and the drug by use of an ordinary plain coating material so that the preparation may float in gastric juice while slowly releasing the drug; however, the preparation of this type has a demerit of having not enough sustained release effect.
On the other hand, Japanese Laid-Open patent publication No. 41320/'79 and Japanese Laid-Open patent publication No. 118414/'80 disclose a sustained release pharmaceutical preparation of oral mucosal adhesion type which comprises lower alkyl ether of cellulose, polyacrylic acid or its pharmaceutically acceptable salt, and drug. This susteined release pharmaceutical preparation has its site of application mainly in the oral cavity and no investigation has yet been made as to its oral administration use.